Anode film layer for galvanic cells



United States Patent 3,092,518 AN ODE FILM LAYER FOR GALVANIC CELLS Nelson C. Cahoon, Fairview Park, and Margaret P. Korver, Brecksville, Ohio, assignors to Union Carbide Corporation, a corporation of New York No Drawing. Filed Mar. 4, 1960, Ser. No. 12,659 18 Claims. (Cl. 136-146) This invention relates to permeable separating media for primary galvanic cells, and more particularly for the so-called dry cells. It relates more particularly to anode film layers comprising such separating media and to methods for their production.

The common form of dry cell comprises a metal anode, a cathode conductor element and an intermediately disposed cathode depolarizer mix which is moistened with an appropriate electrolyte. Separating media are required to be interposed between the anode and the depolarizer mix to prevent internal short circuits of the electrodes, but it is also necessary in the interests of economical and satisfactory operation that the separator media be ionically permeable to permit passage of electrolyte and soluble products of decomposition of the anode.

-A generally accepted requirement for such separator media is that they comprise on one surface a material which when disposed in contact with the anode, and when Wetted with electrolyte, will firmly adhere in moist, sticky relation to the anode. This may be termed the anode film layer or portion of the separator medium. The anode film portion being at least partially soluble or capable of migration in the electrolyte, an electrolyteinsoluble film portion or zone is required to protect the relatively soluble anode film portion or zone from migration from the anode. This electrolyte-insoluble portion may be termed the barrier film portion or zone. It is essential that each of these portions or zones be ionically permeable to allow passage of electrolyte and electrolyte-soluble anode decomposition products through them. A further requirement of the barrier layer is that it does not allow transfer of the anode film components to the cathode.

It is an object of the present invention to provide an anode film particularly adapted for employment in dry cells. It is a further object to provide a method for satisfaotorily bonding such anode film portion to a barrier film portion to provide a unitary separator film. It is a still further object to provide a means facilitating application of an anode film layer to a metal anode.

The anode layer of the invention is prepared by dissolving a predetermined quantity of a binder consisting of a polymerized ester of an unsaturated alcohol and an acid in a low molecular weight organic solvent. Next, a quantity of an electrolyte-soluble, Water-swellable colloid is suspended in the solution. The binder here holds the colloid particles in place on the anode or on the separator support. The suspension can be spread, poured, or painted onto a support sheet of plastic, paper or on the anode metal itself.

Suitable readily hydrolyzed polymerized esters of unsaturated alcohols and acids include the polyvinyl, polyacrylic, polymethacrylic and polymaleic esters of low mo lecular weight acids, such as formic, acetic, propionic acids as well as copolymers of the foregoing, such as those of polyvinyl acetate and polyallyl acetate. A particularly useful and desirable member of the group of esters of polymerized unsaturated alcohols is polyvinyl acetate. The amount of binder used may be varied widely, depending on many factors, including the molecular weight of the selected resin, the solubility in the selected solvent, and the colloid concentration desired for the intended application. Generally, the binder will con- 3,092,518 Patented June 4, 1963 stitute from about 1 to about 10 percent by weight of the colloid-resin-solvent mixture.

Examples of low molecular weight organic solvents are acetone, ethyl ether, ethyl alcohol, chloral, chloroform, cyclopentane heptane, hexane, cyclohexane pentane, dioxane and generally low molecular weight alcohols, ketones and others which are compatible with the selected hydrolyzable polymerized ester.

Generally, the solvent can be chosen solely on the basis of its solvent power for the resin selected and for the insolubility of the colloid therein. Economic, solvent recovery and toxicity factors Will also influence solvent selection.

The colloids found operative in this invention must be compatible with cell electrolytes, must not be readily oxidized by the cell cathode, must not be readily hydrolyzed by cell electrolyte, must not be swollen by organic solvents, and must swell in cell electrolyte. Suitable colloids or colloid-fiormin g materials include methyl cellulose ether, carboxymethyl methyl cellulose, sodium carboxymethyl cellulose, polyvinyl alcohol, hydroxy propyl methyl cellulose, the calcium salts of the copolymer of maleic an hydride and vinyl acetate and equivalent materials as well as various gums. As employed herein, gums refers to a class of colloidal substances, glutinous when moist, but hardening on drying, exuded by or extracted from plants. Suitable gums and gum-like materials include guar gum, locust bean gum, gum karaya, gum tragacanth, low methoxy pectin and gelatin. Mixtures of the foregoing are also very attractive for given applications as one ingredient can be used to provide the viscosity desired for handling, while the second component provides the necessary adhesive characteristics. Depending upon the use requirements, and on the specific colloid, the amount thereof will range from about 5 to about 20 percent by weight of the colloid-resin-solvent mixture.

One of the particular advantages of the present invention is that it enables the casting of suitable anode films on an electrolyte-insoluble barrier film, a metal anode or other support from high solids content suspensions.

As an example of the method of forming the anode film layer of the present invention, particles of watersoluble methyl cellulose are suspended in an acetone solution of polyvinyl acetate and applied to the barrier film, a metal anode or a film-forming support. The acetone is then substantially evaporated, and the remaining film comprising Water-soluble methyl cellulose ether and polyvinyl acetate results. Surprisingly, the presence of polyvinyl acetate in the anode film layer does not alter-or substantially aifect the ability of the anode film to maintain adherence to the metal anode, nor does it interfere with or affect the operation of'a galvanic cell in which it is incorporated. in the anode film of this embodiment, the polyvinyl acetate serves as a compatible binder for Water-soluble methyl cellulose particles or fibers, and the resulting anode fihn, which is a mixture of water-soluble methyl cellulose and polyvinyl acetate, is well adapted to production of dry cells having long and satisfactory shelf life and service life.

Various grades and types of methyl cellulose may be employed according to this invention. Satisfactory watersoluble methyl cellulose should have a methoxy content of at least 27 percent. Various viscosity grades of methyl cellulose ether may be employed, but in general viscosity grades of l000 to 4000 cps. are preferred.

Various types and grades of polyvinyl acetate maybe employed. However, those types are preferred which give a relatively tack-free film upon evaporation of solvents. In general, a polyvinyl acetate having a softening point of C. or above is preferred, although polyvinyl ace- 3 tate having a somewhat lower softening point may also be used.

It will be understood that upon volatilization of the acetone or of the other lower aliphatic oxygenated organic compounds, they may be recovered for re-use. Various solvent recovery methods will occur to one skilled in the art. 7

EXAMPLE 1 To 50 ml. of acetone there is added 3 grams of polyvinyl acetate with rapid agitation. Agitation is continued until the polyvinyl acetate is dissolved. Then, 9.52 grams of 4000 cps. Water-soluble methyl cellulose ether is slowly stirred in. One ml. of water was added to facilitate suspension of the methyl cellulose. The solution was then poured onto a barrier film consisting of cast alkalisoluble methyl cellulose which had a 10.2 percent methoXy content, and which was supported on a horizontal glass plate. The acetone rapidly evaporated from the suspension and a unitary film resulted having a barrier film portion consisting of alkali-soluble methyl cellulose and an anode film portion comprising water-soluble methyl cellulose and polyvinyl acetate.

EXAMPLE 2 Three grams of polyvinyl acetate were dissolved in 300 ml. of acetone, and in this solution were suspended 9.52 grams of No. 1350 Hydrophil (karaya gum). This suspension was evenly poured onto high wet strength alpha cellulose paper (S-17), which had been previously dampened and taped onto a 300 sq. in. glass plate. When solvent evaporation had occurred, a dry smooth composite film resulted. These are only two of the methods by which the anode film may be app-lied. Others include brush-type applications, dough-roll coating applications, and perhaps many more not herein mentioned. If a smoother suspension of the colloid-resin mixture is desired, it may be ball milled for any desired length of time. 7

Similarly, a representative group of separators was prepared using quantities of materials listed in Table I below.

Table I GOIHPOSITION OF ANODE FILM LAYERS APPLIED TO VARIOUS SUPPORT LAYERS Resin and quantity Solvent and volume 150 ml. carbon tetrachloride.

3 g. polyvinyl acetate 50 ml. ethylene dichloride.

3 g. polyvinyl formal" 3 g. polyvinyl acetate. 300 ml. acetone.

3 g. Hereose S (cellulose 200 ml. ethyl acetate.

acetate sorbate). 3 g. polyvinyl acetate 300 ml. acetone. do Do a Do: 5.7 g. polyvinyl acetate.-- 81 ml. acetone. 6.0 g. polyvinyl acetate 70 ml. acetone.

Colloid and quantity of 7 Support layer anode layer or barrier Alkali-soluble methyl cellulose. Stidicum cellulose sul- 9.52 g. oarhoxy-methyl methyl cellulose.

- 9.52 g. water-soluble sodium carboxy methyl cellulose.

9.52 g. Gum karaya 9.52 g. hydroty propyl methyl cellulose.

8. S-17 paper. Do.

9.52 g. calcium salt of copolynier D0.

of maleic anhydride and vinyl acetate. 6 do Do. 7 9.52 g. locust bean gum Do. 80 3 g. 4,000 cps, water soluble Z1110.

methyl cellulose. 86 Do.

N ore-The quantities given in Examples 1 to 6 above were combined and used to coat an approximate 300 sq. in. area.

, A small sample of each of these separator preparations was placed in Leclanch cell electrolyte consisting of 23 percent zinc chloride, 28 percent ammonium chloride, and 49 percent water to determine the length of time required for complete disintegration of the resinbonded colloid layer. These data are shown in Table II. Ordinarily, if 4000 cps. water soluble film is placed in this electrolyte, it will disintegrate within 15 minutes. It may be noted that a somewhat longer period is required in this film where hydrolysis or deterioration of the resin binder must occur before the colloidal material may be released. It should be noted, too, that the products of resin breakdown themselves may aid in the promotion of a sticky, anode contact.

Table II CODLPOSITION AND SOLUBILITY OF SUPPORTED ANODE FILM LAYERS IN LECLANCHE CELL ELE CTROLYTE Example No. Disintegration time in dry cell electrolyte 1 day.

Do. Do. Do. D

o. After 2 days film had not disintegrated, but was 1 (ll/61y sticky and a gelatinous mass.

The separators identified may use a flexible supporting sheet on which the resin-colloid-solvent anode film portion can be spread. In addition to the materials above indicated, the support, in an alkaline cell, may consist of a Woven or non-woven sheet of plastic fibers, rayon or nylon. Laminated support layers also may be used. Thus, a paper base layer may be first coated with a filmforming resin and dried, and then coated with the resinbonded colloid layer.

7 Separators made as above were placed in a dry cell consisting of pre amalgamated zinc cans with the resincollolid film intermediate the depolarizer mix and the anode To follow the rate at which hydrolysis or degradation of the resin occurred, voltage and amperage readings on the fresh cells were made periodically. These readings are shown in Table III.

Table III RAPIDITY on HYDROLYSIS IN EXPERIMENTAL LECLANCHE CELLS Voltage and amperage readings Example No. Approilra5 hrs. 3 Days 2 Weeks V. A. V. A. V. A.

Table IV SHELF AND SERVICE SUMMARY O'N FIRST EXPERI- MENTAL CELLS MADE WITH PVAc, 4000 CPS. METHOCEL, ALKALI SOLUBLE ANODE FILM LAYER Service test 4-ohm, 4-Min. RIF-Minutes to 2 Weeks 6 Mos. 12 Mos. 21 0. Shelf V. A. V. A. V. A.

Experimental 1. 54 3 9 1. 60 4. 4 1. 60 4. 8 Control 1. 64 6.1 1.60 5.1 1. 59 4. 6

Service Test 4-ohm, 4-Min. LIF- 2.25-ohm LIF- Minutes to 1.1, 0.9, 0.8 v. Minutes to 0.65 v.

Experimental--." (496) (858) (1,117) 634 ontrol (528) (1,013) (1,136) 593 24 Mos. 36 Mos. 48 Mos. 60 Mos. 21 0. Shelf V. A. V. A. V. A. V. A.

Experimental--. 1. 59 3. 9 1. 56 4. 2 1. 57 4. 6 1. 53 3. 7 Control 1. 59 3. 7 1. 57 3. 5 No more cells avaiable Although their initial voltage and amperage values were not quite as high as the control cells, they did have extremely good voltage and current maintenance even after five years storage. The cells used for control were filmlined laboratory assembled cells. They contained 4000 cps, water-soluble Methocel, anode film, with mercuric chloride amalgamating agent, used in combination with alkali-soluble methyl cellulose barrier film.

In another embodiment of the invention, a suspension was made up by the formulae presented in Table IExamples 8a and 8b. The suspension was painted directly onto the inside of the zinc can and then dusted with a little additional 4000 cps., water-soluble methyl cellulose and dried. The barrier layer, in the form of an aqueous solun'on of sodium cellulose sulfate, and bobbin were then added. The service date of these cells as compared with the factory product cells are presented in Table V. These data compare favorably, and visual inspection of the discharged cells showed that a very good contact existed between the anode film and the zinc can, thus proving that the anode film can be successfully applied to a zinc anode surface.

Table V COMPARISON OF INITIAL SERVICE DATE OF EXPERI- MENTAL FILM ON ANODE LINED WITH FACTORY PRODUCT PASTE-LINED 0 SIZE, CELLS A major advantage of the present invention is that the anode film thereof can be tailor-made from a great variety of resins and colloids so as to be useful in many cell systems employing diverse anodic materials including zinc and magnesium as Well as various electrolytes.

The invention has other advantages. Not only are 6 cells of excellent quality produced thereby, but the lining of the anodes can be carried out in an economical way well adapted to automatic machines. Moreover, the invention permits a conforming lining to be applied to anode surfaces of any shape.

This application is a continuationinpart of application Serial No. 549,161, filed November 25, 1955, and now abandoned.

What is claimed is:

11. A method for producing an anode film portion of a separator medium galvanic cells, which method comprises suspending at least one water-swellable organic colloid in a volatile low molecular weight organic compound containing a readily hydrolyzed polymerized ester of an unsaturated alcohol, applying said suspension to a support and removing said organic compound by volatilizetion.

2. A method for producing an anode film portion of a separator medium for galvanic cells, which method comprises suspending an electrolyte-soluble, water-swellable organic colloid in a volatile low molecular weight organic compound containing a readily hydrolyzed polymerized ester of an unsaturated acid, applying said suspension to a support and removing said organic compound by volatilization.

3. A method for producing an anode film portion of a separator medium for galvanic cells, which comprises suspending an electrolyte soluble, Water swellable organic colloid in a volatile low molecular weight oxygenated aliphatic organic compound containing a readily hydrolyzed polymerized ester of an unsaturated alcohol, applying said suspension to a support and removing said low molecular 'Weight oxygenated aliphatic organic compound by volatilization.

4. The method of claim 3, wherein the low molecular Weight oxygenated aliphatic organic compound is acetone.

5. The method of claim 3, wherein the low molecular weight oxygenated aliphatic organic compound is ethyl ether.

6. The method of claim 3, wherein the low molecular weight oxygenated aliphatic organic compound is ethyl alcohol.

7. The method of claim 3, wherein the readily hydrolyzed polymerized ester of an unsaturated alcohol is polyvinyl acetate.

8. A method for producing an anode film portion of a separator medium for galvanic cells, which comprises suspending an electrolyte-soluble, water-swellable organic colloid in a volatile low molecular weight oxygenated aliphatic organic compound containing a readily hydrolyzed polymerized ester of an unsaturated alcohol, applying said suspension to a metal anode for a galvanic cell, and removing said oxygenated aliphatic organic compound from said suspension by volatilization.

'9'. The method of claim 8, wherein the anode metal is a metal selected from the group consisting of zinc, magnesium and alloys thereof.

10. A method for producing a separator medium for galvanic cells, which comprises suspending an electrolytesoluble, water-swellable organic colloid in a volatile low molecular weight oxygenated aliphatic organic compound containing a readily hydrolyzed polymerized ester of an unsaturated alcohol, applying the resulting suspension to a adapted to serve as a barrier film portion tor galvanic cells, and removing said oxygenated aliphatic organic compound from said suspension by volatilization.

11. -A separator medium for galvanic cells comprising a barrier film portion having bound thereto an anode film portion of an unsaturated ester and at least one watersoluble organic colloid selected from the group consisting of carboxymethyl methyl cellulose, sodium carboxymethyl cellulose, hydroxymethyl cellulose, hydroxypropyl methyl cellulose, calcium salts of the copolymer of maleic anhydride and vinyl acetate, gum karaya, guar gum, locust bean gum, polyvinyl alcohol, pectin and mixtures thereof.

'12. -A method for producing an anodefilm portion of a separator medium for galvanic 'cells, which method comprises suspending water-soluble methyl cellulose other in a volatile low molecular weight organic compound containing a readily hydrolyzed polymerized ester of an unsaturated alcohol, applying said suspension to a support and removing said organic compound by volatilization. i

13. A method for producing an anode film portion of a separator medium for galvanic cells, which method com prises suspending water-soluble methylcellul-ose ether in a volatile low molecular weight organic compound containing a readily hydrolyzed polymerized ester of an unsaturated acid, applying the resulting suspension to a support and removing said organic compound by volatilizati'on. f

114. A method for producing an anode film portion of a separator medium for galvanic cells, which comprises suspending at least one waiter-soluble methyl cellulose ether in a volatile low molecuar Weight oxygenated aliphatic organic compound containing a readily hydrolyzed polymerized ester of an unsaturated alcohol, applying the resulting suspension to a support and removing said low molecular weight oxygenated aliphatic organic compound by volatilization.

15. The method of claim 14, wherein the low molecular Weight oxygenated aliphatic organic compound is acetone.

16. An anode film portion for galvanic cells comprising a readily hydrolyzed polymerized ester of an unsaturated alcohol and a water-soluble methyl cellulose ether.

17. An anode film portion for galvanic cells comprising a Water-soluble methyl cellulose ether in admixture with a polyvinyl car boxylate.

18. A separator medium for galvanic cells comprising a barrier film portion having in securely bound relation thereto, an anode film portion comprising water-soluble methyl cellulose ether in admixture with a polyvinyl carboxylate.

References Cited in the file of this patent UNITED STATES PATENTS 2,231,319 Burgess Feb. 11, 1941 2,534,336 Cahoon Dec. 19, 1950 2,741,650 Lukman et al Apr. 1 0', 1956 2,747,009 Kirlcwood et a1 May 22, 1956 2,772,322 Witt et a1. Nov. 27, 1956 2,809,945 Wright et a l Oct. 15, 1957 

1. A METHOD FOR PRODUCING AN ANODE FILM PORTION OF A SEPARATOR MEDIUM GALVANIC CELLS, WHICL METHOD COMPRISES SUSPENDING AT LEAST ONE WATER-SWELLABLE ORGANIC COLLOID IN A VOLATILE LOW MOLECULAR WEIGHT ORGANIC COMPOUND CONTAINING A READILY HYDROLYZED POLYMERIZED ESTER OF AN UNSATURATED ALCOHOL, APPLYING SAID SUSPENSION TO A SUPPORT AND REMOVING SAID ORGANIC COMPOUND BY VOLATIZATION. 